1. Field of the Invention
The present invention relates to an object-holding apparatus mounted in the process chamber of a plasma processing apparatus or the like to hold an object to be processed.
2. Description of the Related Art
Generally, as an apparatus for processing a substrate to be processed such as a semiconductor wafer with a plasma, for example, a CVD apparatus, an etching apparatus and the like, and an ashing apparatus and the like for removing a resist mask are known widely.
This plasma processing apparatus has a process chamber where plasma is generated in a process gas-introduced atmosphere so as to process a loaded substrate to be processed. A holding apparatus for holding the substrate to be processed while functioning as an electrode for generating the plasma is set in the process chamber.
FIG. 5 shows an arrangement of a conventional holding apparatus.
This holding apparatus is formed of a susceptor (holder main body) 1 on which a semiconductor wafer (to be referred to as a wafer hereinafter) W as an object to be processed is to be placed, an electrostatic chuck 2 arranged on the upper surface (the upper surface of a convex portion) of the holder main body 1, and a focus ring 3 fitted on a flange surrounding the electrostatic chuck 2. The upper surface of the focus ring 3 has a groove (step) to fit with the placed wafer W.
The holder main body 1 has a gas supply path 6 through which a gas is introduced from the outside to control the temperature of the wafer W. The gas supply path 6 is formed of a trunk portion 6a connected to an external gas supply source (not shown) and branch portions 6b branching from the trunk portion 6a and extending through the electrostatic chuck 2 to connect to a plurality of openings 7 formed in the upper surface of the electrostatic chuck 2.
The gas supply source supplies helium gas or the like that serves as a heat transfer medium (cooling medium) to control the temperature of the held wafer. An RF power supply 4 is connected to the holder main body 1 to supply RF power to it. The electrostatic chuck 2 is formed as a sheet-like dielectric made of a polyimide resin or the like. An electrode plate 8 connected to a DC power supply 5 is formed in the electrostatic chuck 2. When the DC power supply 5 applies a DC voltage to the electrode plate 8, an attracting force such as the Coulomb force is generated and the wafer W is electrostatically attracted to the holder main body 1.
Usually, in the process with the plasma processing apparatus, the wafer W is attracted to the electrostatic chuck 2 and held by it. The process chamber is evacuated by an exhaust system (not shown) to a predetermined vacuum degree, and a process gas is introduced there. After that, the RF power supply 4 applies RF power to the holder main body 1 so the holder main body 1 serves as an electrode, thus generating a plasma between the holder main body 1 and an opposing electrode (not shown). The plasma converges on the wafer W through the focus ring 3 on the holder main body 1, and subjects the wafer W to a predetermined plasma process (e.g., an etching process). This process of exposing the wafer to the plasma increases the temperature of the wafer W. When the helium gas (described above) is sprayed to the lower surface of the wafer W through the openings 7, the wafer W can be cooled efficiently.
In this holding apparatus, however, the focus ring 3 is merely fitted on the holder main body 1 considering maintenance and the like. A narrow vacuum gap is present between the focus ring 3 and holder main body 1 to degrade heat transfer between them, and they cannot be cooled well like the wafer W. Hence, as the process of the wafer W progresses, the temperature of the focus ring 3 is stored over time, and exceeds the temperature of the wafer W.
Due to this adverse influence, the etching characteristics of the peripheral portion of the wafer W change to etch this portion insufficiently. Then, for example, the hole-making readiness may be degraded, or the etching selectivity may be decreased. The hole-making readiness mean the characteristics indicating whether etching to a predetermined depth can be performed reliably. If the hole-making readiness is poor, that is, a contact hole, for example, cannot be made by etching to a predetermined depth.
Particularly, these days, increases in diameter and micropatterning degree of the wafer W are strongly demanded in order to increase the production amount and to improve the packing density. Also, a high yield standard is also demanded. Devices are arranged on the wafer W until very close to its circumference, so that a layout with which the number of chips that can be formed per wafer W can be increased as much as possible can be obtained. As a result, the temperature increase of the focus ring 3 largely adversely affects the yield of the devices.
As means for solving this problem, Jpn. Pat. Appln. KOKAI Publication Nos. 7-310187 and 10-303288 (U.S. Pat. No. 5,958,265) propose various methods that adjust the temperature of a member corresponding to the focus ring.
Of these references, Jpn. Pat. Appln. KOKAI Publication No. 10-303288 discloses a technique of attracting a focus ring (character correction ring) by electrostatic attraction to improve the contact, so that heat conduction is improved and the focus ring cooling effect is increased. In this prior art, however, the focus ring has a complicated shape, and it is cumbersome to form it. A thin portion such as a flange tends to deform when heat expansion or contraction acts on it. When this deformation occurs, the contact with the cooling surface degrades, to sometimes hinder cooling.
Regarding electrostatic attraction of the focus ring and the wafer W, attraction and release are performed simultaneously by one power supply. Thus, when the wafer W is to be loaded on or removed from the electrode, the focus ring sometimes floats. When the focus ring floats to come into contact with the transfer mechanism, a transfer error may occur. In view of this, this prior art has a mechanical clamp mechanism. Thus, the focus ring is urged against the holder main body further tightly, so that the cooling effect is obtained, and floating can be prevented. However, the mechanical mechanism has a driving mechanism and a detachable connecting mechanism such as a clamper. Accordingly, the mechanical mechanism has a complicated structure. This increases the cost.
It is an object of the present invention to provide an object-holding mechanism which is mounted in an apparatus that processes an object to be processed with a plasma, suppresses heat accumulation, and eliminates a change in plasma processing characteristics over time in the vicinity of a focus ring, so that the entire surface of the object to be processed can be processed uniformly, and cost reduction can be realized with a simple structure.
In order to achieve the above object, the present invention provides an object-holding apparatus comprising a holder main body which internally includes a temperature adjusting mechanism and forms a convex shape, and has a holding portion on an upper surface of a convex portion where an object to be processed is to be placed and a flange formed on a peripheral portion of the holding portion in order to fit with a focus ring, a first dielectric film which is formed on the holding portion and generates a Coulomb force for attracting the object to be processed upon application of a DC voltage, a second dielectric film which is formed on the flange and generates a Johnson-Rahbek force for attracting the focus ring upon application of a DC voltage, and a DC power supply which applies DC voltages to the first and second dielectric films, wherein the temperature adjusting mechanism adjusts the focus ring and the object to be processed held by the holding portion to almost the same temperature.
An object-holding apparatus has a holder main body which internally includes a temperature adjusting mechanism and forms a convex shape, and has a holding portion on an upper surface of a convex portion where an object to be processed is to be placed and a flange formed on a peripheral portion of the holding portion where a focus ring is to be fitted, a first dielectric film which is formed on the holding portion and generates a Coulomb force for attracting the object to be processed upon application of a DC voltage, a second dielectric film which is formed on the flange and generates a Johnson-Rahbek force for attracting the focus ring upon application of a DC voltage, a DC power supply which applies DC voltages to the first and second dielectric films, and a switch which is formed between the first dielectric film and the DC power supply and is electrically connected when the object to be processed is to be processed and electrically disconnected when the object to be processed is to be transferred, wherein the focus ring is attracted and held when the object to be processed is to be transferred as well.